Before everyone starts flipping out over whats "OP"
Maybe you should realize that counterpicks exist for a reason. If something is popular you probably have a 25-30% chance of seeing it in gameplay. Those chances are pretty high and are probably worth counterpicking for.
This game has a cyclical meta where champions rise in favor in response to other champions that were previously favorable. A few months ago I admit I only saw 1 or 2 zeds, most didn't do well at all, not many people complained about zed and he was no different than he was now. Now everyone flips out when they lose to a zed and claim he's "broken". But I predict that in a few months, if zed doesn't get nerfed to oblivion everyone will probably be complaining about kayle and malzahar again (yall are aready starting to complain about lissandra).
I'm not saying that some champion kits are broken, they are but it doesn't mean that they wont fall out of favor again. So just either stop playing until things change or learn to counterpick popular champions.
And no, I'm not just defending all those OP champions that I play (because I don't play them). I just truly believe that they are not OP. I even just lost a game to an 30/10/16 akali, but I still don't think she's OP.

-

isn't listed in most places but I consider it a hard counter
i've found is very good vs zed. You have E harass if he goes to aa minions. Q + W I would save if he decides to go offensive, but
landing the W can turn the fight. Cast Q before he ports and chase him down.
cuz he kinda owns all assassins.
seems to go even with him and kinda beats him early game but my favorite counter to zed is
. Just e to him when he casts w and combo with q auto and w. Rinse and repeat. Works pretty well and when he ults you, use yours and stay invis till the end of its duration, e to him and cut his head off.

Just a small list of champions who can easily annihilate Zed pre 6 and survive his all in at level 6.